Esters of aliphatic alcohols and aromatic carboxylic acids are widely used in chemical industry, particularly as plasticizers and as intermediates in the preparation of polyester resins.
However, the rate of esterification reaction is usually quite slow; therefore catalysts have been used to increase the esterification reaction rate. The esterification process can be carried out using liquid catalysts such as sulfuric acid, sulfonic acid, or p-toluenesulfonic acid (liquid phase esterification reaction using liquid catalyst); a cationic ionic exchange resin as a catalyst (liquid phase esterification reaction using solid catalyst); and liquid phase acids carried by a solid carrier, and zeolite as a catalyst (gas phase esterification reaction).
Esterification reaction using sulfonic acid, hybrid inorganic solid acid material, Bronsted acidic ionic liquids, and Bronsted acid surfactant-combined catalyst (BASC) are also known in the art.
One of the problems associated with liquid-phase esterification reaction by the liquid catalyst is that the acidic liquid catalysts such as sulfuric acid or p-toluenesulfonic acid can cause corrosion problems to the reactor. These liquid acid catalysts are also discharged along with the reaction products, thus causing severe waste disposal and pollution problems. The commonly used active catalysts such as sulfuric acid, hydrochloric acid, and aluminum sulfate promote rapid reaction rates but have the serious drawback, in that they lead to considerable alcohol loss by ether formation.
Therefore, there is a need for a simple process of esterification which mitigates the drawbacks associated with the conventional processes.